Gas turbine engine and methods of controlling emissions therefrom

ABSTRACT

A gas turbine engine that includes a stage of guide vanes, a compressor downstream from the stage of guide vanes, and a combustor downstream from the compressor. The combustor includes a primary combustion zone and a secondary combustion zone downstream from the primary combustion zone. The primary combustion zone includes an exit configured to channel combustion gases towards the secondary combustion zone. A controller is communicatively coupled with the stage of guide vanes, the controller configured to monitor a temperature at the exit of the primary combustion zone, and selectively open and close the guide vanes to maintain the temperature within a predefined temperature range.

BACKGROUND

The present disclosure relates generally to gas turbine engines and,more specifically, to systems and methods of controlling emissions froma gas turbine engine having axial fuel staging (AFS) multi-stagecombustors.

Many known combustion turbine engines burn a fuel-air mixture in acombustor assembly to generate a combustion gas stream that is channeledto a turbine assembly. The turbine assembly converts the energy of thecombustion gas stream to work that may be used to power a machine, suchas an electric generator. Typically, when a turbine is operated at arelatively high load, the combustor exit temperature of the gas streamis high and carbon-monoxide (CO) and/or unburned hydrocarbon (UHC)emissions may be effectively controlled. However, when the combustionprocess is not fully completed, undesirable levels of CO and/or UHC maybe present in the turbine exhaust system. In typical combustion turbineengines, the ability of the hydrocarbon fuel to completely combust atleast partially based on a lower limit on the combustor exittemperature. As the turbine load decreases (often referred to as “turndown”), in many gas turbines it is necessary to reduce the combustorexit temperature, which may undesirably result in increased levels of COand UHC being formed. Accordingly, it is desirable to maintain highcombustor temperatures as a turbine engine reduces its load.

BRIEF DESCRIPTION

In one aspect, a gas turbine engine is provided. The gas turbine engineincludes a stage of guide vanes, a compressor downstream from the stageof guide vanes, and a combustor downstream from the compressor. Thecombustor includes a primary combustion zone and a secondary combustionzone downstream from the primary combustion zone. The primary combustionzone includes an exit configured to channel combustion gases towards thesecondary combustion zone. A controller is communicatively coupled tothe stage of guide vanes, the controller configured to monitor atemperature at the exit of the primary combustion zone, and selectivelyopen and close the guide vanes to facilitate maintaining the temperaturewithin a predefined temperature range.

In another aspect, a gas turbine engine is provided. The gas turbineengine includes a stage of guide vanes, a compressor downstream from thestage of guide vanes, and a combustor downstream from the compressor.The combustor includes a primary combustion zone and a secondarycombustion zone downstream from the primary combustion zone. The primarycombustion zone includes an exit configured to channel combustion gasestowards the secondary combustion zone. A controller is communicativelycoupled to the stage of guide vanes, the controller configured tomonitor a temperature at the exit of the primary combustion zone,determine a combustion mode in which the combustor is operating, andselectively open and close the guide vanes to facilitate maintaining thetemperature at a temperature threshold associated with the combustionmode in which the combustor is operating.

In yet another aspect, a method of controlling emissions from a gasturbine engine that includes a compressor and a combustor is provided.The method includes monitoring a temperature within the combustor of thegas turbine engine, wherein the combustor includes a primary combustionzone and a secondary combustion zone downstream from the primarycombustion zone, the temperature monitored at an exit of the primarycombustion zone. The method also includes determining a combustion modein which the combustor is operating, and selectively opening and closingguide vanes upstream of the compressor to facilitate maintaining thetemperature at a temperature threshold associated with the combustionmode in which the combustor is operating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary gas turbine engine.

FIG. 2 is a cross-sectional illustration of an exemplary combustor thatmay be used in the gas turbine engine shown in FIG. 1.

FIG. 3 is a flow diagram illustrating an exemplary method of controllingemissions from a gas turbine engine.

DETAILED DESCRIPTION

The embodiments described herein relate to systems and methods ofcontrolling emissions from a gas turbine engine having axial fuelstaging (AFS) multi-stage combustors. For example, the emissions may becontrolled by modulating the inlet guide vanes or variable guide vaneson the compressor of the gas turbine engine, thereby modulating airflowinto the multi-stage combustor. Modulating the airflow facilitatescontrolling the intra-stage temperature of the multi-stage combustor,which is a significant factor in emissions control. In the exemplaryembodiment, the selective positioning of the guide vanes is controlledautomatically by a Proportional-Integral (PI) controller. A detailedphysics-based model for the gas turbine engine is used to calculateand/or estimate a temperature at an exit of a primary combustion zone ofthe multi-stage combustor, and this determined temperature is providedto the closed loop controller. Accordingly, a desired exit temperaturemay be dynamically enforced by modulating the guide vanes. The desiredexit temperature may be a constant value, or may be varied in accordancewith a schedule that corresponds to physical conditions within thecombustor. Controlling and maintaining the desired temperature within apredefined range facilitates enhancing emissions control, such as whenthe gas turbine engine is in a transient operational state. In addition,selective modulation of the guide vanes may be used to operate thecombustor at reduced temperatures for reducing thermal strain on thecombustion system and increasing part life.

Unless otherwise indicated, approximating language, such as “generally,”“substantially,” and “about,” as used herein indicates that the term somodified may apply to only an approximate degree, as would be recognizedby one of ordinary skill in the art, rather than to an absolute orperfect degree. Accordingly, a value modified by a term or terms such as“about,” “approximately,” and “substantially” is not to be limited tothe precise value specified. In at least some instances, theapproximating language may correspond to the precision of an instrumentfor measuring the value. Additionally, unless otherwise indicated, theterms “first,” “second,” etc. are used herein merely as labels, and arenot intended to impose ordinal, positional, or hierarchical requirementson the items to which these terms refer. Moreover, reference to, forexample, a “second” item does not require or preclude the existence of,for example, a “first” or lower-numbered item or a “third” orhigher-numbered item.

FIG. 1 is a schematic illustration of an exemplary gas turbine engine100. In the exemplary embodiment, gas turbine engine 100 includes aninlet duct 102, a stage 104 of guide vanes, a compressor 106, acombustor 108, and a turbine section 110 coupled in a serial flowrelationship. Intake air 112 is channeled through duct 102 and throughstage 104 of guide vanes, prior to it being directed towards compressor106. Compressor 106 compresses intake air 112 and discharges compressedair 114 towards combustor 108. A fuel injection system 116 provides fuel118 to combustor 108, and the resulting fuel-air mixture is ignitedwithin combustor 108. Combustion gas 120 is discharged from combustor108 and is directed towards turbine section 110 where the thermal energyof combustion gas 120 is converted to work. A portion of the work isused to drive compressor 106, and the remaining balance is used to drivean electric generator 122 to generate electric power.

In the exemplary embodiment, gas turbine engine 100 includes multiplesensors 124 for detecting various conditions of the gas turbine engine100, generator 122, and the ambient environment. Example sensors 124include temperature sensors, pressure sensors, and the like. Temperaturesensors may monitor compressor discharge temperature, turbine exhaustgas temperature, and/or other temperature measurements of the gas streamthrough gas turbine engine 100. Pressure sensors may monitor static anddynamic pressure levels at the compressor inlet and outlet, the turbineexhaust, and/or at other locations within gas turbine engine 100.Sensors 124 may also include, but is not limited to including, flowsensors, speed sensors, flame detector sensors, valve position sensors,guide vane angle sensors, and the like, that sense various parameterspertinent to the operation of gas turbine engine 100. Typically,pressure, temperature, flow, speed, guide vane angle and many othersensors on a gas turbine are reliable, require infrequent calibrationand maintenance, and are relatively inexpensive. However, it isgenerally difficult to directly monitor combustion gas or combustordischarge temperatures, such as with a thermocouple, due to the harshcharacteristics of the combustion gas. As described above, combustortemperature is a significant factor in emissions control.

In the exemplary embodiment, a controller 126 receives feedbacktransmitted from sensors 124 and controls operation of gas turbineengine 100 based on the feedback. Controller 126 may be a computersystem having a processor(s) that executes programs to control theoperation of gas turbine engine 100. The operation may be controlledusing sensor feedback, instructions from human operators, and/orcombustor temperature estimates that may be determined based on thesensor feedback. In one embodiment, controller 126 estimates and/orcalculates the combustion gas or combustor discharge temperatures usinga physics-based model that receives the sensor feedback as inputs. Thecombustion gas or combustor discharge temperatures estimates may bebased on at least an airflow output from compressor 106, a fuel flowinput to combustor 108, and/or an operational status of an inlet bleedheat (IBH) system 128. The airflow output from compressor 106 isdependent at least partially on the angle of the guide vanes in stage104 that regulate airflow into compressor 106.

In combustion systems having a single combustion stage, the modelassumed that all fuel was burned in a single combustion chamber. Withaxial fuel staging, the current model uses valve position and fuelpressure data to determine fuel flows, and thus a ratio between theprimary and secondary combustion fuel flows. Therefore, a certainpercentage of the fuel is burnt in the first combustion chamber with afirst determined airflow, and the remaining percentage of the fuel isnow modeled to be burnt in the second combustion chamber with a seconddetermined airflow. The second determined airflow may include someadditional airflow (such as cooling flows) which are provided to thesecond combustion chamber without passing through the first combustionchamber.

In operation, controller 126 regulates total fuel flow, the relativeposition of inlet guide vanes (or alternatively and/or additionallyvariable guide vanes within compressor 106), the operational status ofIBH system 128 (i.e., airflow extraction rate from compressor 106), andcombustor fuel splits to achieve a desired cycle match point (i.e., togenerate a desired power output and heat-rate while observingoperational boundaries). Total fuel flow and guide vane position aresignificant factors in achieving the desired result. A typical partialload or transient status control mode includes setting the fuel flow andthe guide vane angles to satisfy a load (generator output) request,while monitoring an exhaust temperature profile (temperature controlcurve). When base load or steady state operation is achieved, the guidevanes are typically positioned at their angle of maximum physical limitfor channeling airflow therethrough. At base load, fuel flow regulationand combustion splits are generally adjusted to achieve an exhausttemperature profile needed to satisfy emission limits and other gasturbine operating limits.

For example, controller 126 is selectively operable to maintain the NOxand CO emissions in the turbine exhaust to within certain predefinedlimits, and to maintain the combustor temperature to within predefinedtemperature ranges. The predefined temperature ranges may be based oncurrent physical conditions within the combustor. For example,controller 126 may selectively control various parameters of gas turbineengine 100, including those described above, to maintain an estimatedcombustion gas or combustor discharge temperature within one of aplurality of predefined temperature ranges. Predefined values ofphysical conditions, or a ranges of predefined values, may correspond toa respective predefined temperature range. In addition, combustor 108 isoperable in one of a plurality of combustion modes based on the currentphysical conditions of gas turbine engine 100. Maintaining the combustortemperature within the respective predefined temperature ranges enablescombustor 108 to operate in a combustion mode for producing a reduceddynamic response and reduced emissions for the current physicalconditions of gas turbine engine 100. When gas turbine engine 100 is ina startup or turn-down transient operating mode, controller 126 may beoperable to dynamically adjust the combustion temperature accordingly.

In the exemplary embodiment, a combination of compressor dischargepressure and temperature at the exit of a primary combustion zone, aswill be described in more detail below, is used to initiate modetransfers. For example, as a turbine load is increased, the exittemperature will be controlled by opening the guide vanes, whichincreases compressor discharge pressure. When a compressor dischargepressure threshold is met, transfer to a higher combustion mode isinitiated, and the turbine loading is controlled based on a new exittemperature value. As a turbine load is reduced, the guide vanes will beclosed and the exit temperature will begin to drop, thereby initiatingtransfer to a lower combustion mode. In alternative embodiments, openingand closing of the guide vanes for exit temperature control may be usedin some, but not all, combustion modes. For example, it may be desirableto control the exit temperature for combustion modes that are active inthe bottom 50 percent of the load range of gas turbine engine 100. IBHsystem 128 may also be used to manipulate the cycle conditions of thecombustor and the exit temperature from the primary combustion zone. Forexample, as a turbine load is reduced, the IBH system 128 may beselectively activated to modify the compressor discharge pressure,thereby providing another form of control for maintaining a desired exittemperature from the primary combustion zone.

FIG. 2 is a schematic illustration of an exemplary combustor 108. In theexemplary embodiment, combustor 108 includes a head end 130, a dischargeend 132, and a combustion chamber 134 defined therebetween. Head end 130includes a primary fuel injector 136 for supplying fuel to combustionchamber 134 from fuel injection system 116. The fuel is mixed with airfrom compressor 106 (shown in FIG. 1), and the fuel-air mixture iscombusted in a primary combustion zone 138. In the exemplary embodiment,primary combustion zone 138 includes an exit 140 that defines a boundarybetween primary combustion zone 138 and a secondary combustion zone 142.Combustion gas 144 is discharged from primary combustion zone 138through exit 140, and is channeled into secondary combustion zone 142.

Within secondary combustion zone 142, combustor 108 includes a pluralityof secondary (i.e., axial fuel staging (AFS)) injectors spacedcircumferentially about combustor 108, and oriented radially relative toan axis of combustion chamber 134. Secondary fuel injectors 146 providefuel from fuel injection system 116 for mixing with combustion gas 144.The additional fuel is combusted within secondary combustion zone 142,and combustion gas 120 is discharged from discharge end 132.

In some embodiments, the additional fuel injected into zone 142 may beprovided from a secondary fuel supply, in which case the secondary fuelor fuels may be different from and more volatile than the fuel providedto primary combustion zone 138 (e.g., any suitable gaseous or liquidfuel, such as, but not limited to, natural gas, liquefied natural gas(LNG), syngas, associated petroleum gas, methane, ethane, butanepropane, biogas, sewage gas, landfill gas, coal mine gas, gasoline,diesel, naphtha, kerosene, methanol, biofuel, and/or any combinationthereof). In some embodiments, the secondary fuel may be the same fuelas the primary fuel. Providing fuel to both primary combustion zone 138and secondary combustion zone 142 facilitates enabling a more completecombustion to be achieved, which may facilitate reducing certainemissions (e.g., NOx emissions) discharged from gas turbine engine 100.

As described above, maintaining the combustor temperature within arespective predefined temperature range enables combustor 108 to operatein a combustion mode while producing a reduced dynamic response and withreduced emissions for the current physical conditions of gas turbineengine 100 (shown in FIG. 1). In the exemplary embodiment, controller126 continuously calculates (i.e., monitors) the temperature at exit 140of primary combustion zone 138, determines a combustion mode in whichcombustor 108 is operating, and controls actuation of stage 104 of guidevanes to facilitate maintaining the monitored temperature within therespective predefined temperature range associated with the determinedcombustion mode. Controlling actuation of the guide vanes regulatesairflow provided to and/or channeled through compressor 106, and thusregulates airflow provided to combustor 108. Reducing airflow tocombustor 108 generally increases combustor temperature, and increasingairflow to combustor 108 generally reduces combustor temperature, whenfuel supply remains constant.

Each respective predefined temperature range is defined by a minimumtemperature threshold and a maximum temperature threshold. In general,emissions are facilitated to be reduced at higher combustiontemperatures. Accordingly, in one embodiment, controller 126 controlsactuation of the guide vanes to maintain the monitored temperature at ornear the maximum temperature threshold of the respective predefinedtemperature range. In other words, the guide vanes are controlled tomaintain the monitored temperature closer to the maximum temperaturethreshold than the minimum temperature threshold. Alternatively, theguide vanes are controlled to main the monitored temperature at adesired temperature threshold within the predefined temperature range toobtain desired emissions or dynamics characteristics.

FIG. 3 is a flow diagram illustrating an exemplary method 200 ofcontrolling emissions from a gas turbine engine. Method 200 includesmonitoring 202 a temperature within the combustor of the gas turbineengine, wherein the combustor includes a primary combustion zone and asecondary combustion zone downstream from the primary combustion zone,the temperature monitored at an exit of the primary combustion zone.Method 200 also includes determining 204 a combustion mode in which thecombustor is operating, and selectively opening and closing 206 guidevanes upstream of the compressor to maintain the temperature at atemperature threshold associated with the combustion mode in which thecombustor is operating.

The embodiments described herein relate to systems and methods ofcontrolling emissions from a gas turbine engine. The emissions arecontrolled by monitoring and dynamically enforcing an exit temperatureof a primary combustion zone in a multi-stage combustor by controllingairflow into the combustor via guide vane control. Accordingly, thesystems and methods described herein facilitate providing betteremissions control, lower turn down, and reduced thermal strain on hotgas path components.

The above description is meant to be exemplary only, and one skilled inthe art will recognize that changes may be made to the embodimentsdescribed without departing from the scope of the invention disclosed.For example, the process steps described herein may be modified induration, temperature, or time between cycles, for example. Still othermodifications, which fall within the scope of the present invention,will be apparent to those skilled in the art, in light of a review ofthis disclosure, and such modifications are intended to fall within theappended claims.

Exemplary embodiments of systems and methods of controlling emissionsfrom a gas turbine engine thereof are described above in detail. Themethods are not limited to the specific embodiments described herein,but rather, steps of the methods may be utilized independently andseparately from other steps described herein. For example, the methodsdescribed herein are not limited to practice with industrial gas turbineengines as described herein. Rather, the exemplary embodiment can beimplemented and utilized in connection with many other applications.

Although specific features of various embodiments of the invention maybe shown in some drawings and not in others, this is for convenienceonly. Moreover, references to “one embodiment” in the above descriptionare not intended to be interpreted as excluding the existence ofadditional embodiments that also incorporate the recited features. Inaccordance with the principles of the invention, any feature of adrawing may be referenced and/or claimed in combination with any featureof any other drawing.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

What is claimed is:
 1. A gas turbine engine comprising: a stage of guidevanes; a compressor downstream from the stage of guide vanes; acombustor downstream from the compressor, the combustor comprising aprimary combustion zone and a secondary combustion zone downstream fromthe primary combustion zone, wherein the primary combustion zonecomprises an exit configured to channel combustion gases towards thesecondary combustion zone; and a controller communicatively coupled tothe stage of guide vanes, the controller configured to: monitor atemperature at the exit of the primary combustion zone; and selectivelyopen and close the guide vanes to facilitate maintaining the temperaturewithin a predefined temperature range.
 2. The gas turbine engine inaccordance with claim 1, wherein the combustor is operable in aplurality of combustion modes, the controller further configured tofacilitate maintaining the temperature within a respective predefinedtemperature range that is associated with each combustion mode.
 3. Thegas turbine engine in accordance with claim 2, wherein each respectivepredefined temperature range is defined by a respective maximumtemperature threshold, the controller further configured to selectivelyopen and close the guide vanes to maintain the temperature at therespective maximum temperature threshold.
 4. The gas turbine engine inaccordance with claim 1, wherein the controller is configured tocalculate the temperature at the exit of the primary combustion zone. 5.The gas turbine engine in accordance with claim 4, wherein thecontroller is further configured to calculate the temperature based onan airflow output from the compressor, a fuel flow input to thecombustor, and an operational status of an inlet bleed heat system. 6.The gas turbine engine in accordance with claim 4, wherein thecontroller is further configured to calculate the temperature using aphysics-based model.
 7. The gas turbine engine in accordance with claim1 further comprising a fuel injection system comprising a primary fuelinjector configured to provide fuel to the primary combustion zone, anda secondary fuel injector configured to provide fuel to the secondarycombustion zone.
 8. The gas turbine engine in accordance with claim 1,wherein the controller comprises at least one of a Proportionalcontroller or a Proportional-Integral (PI) controller.
 9. A gas turbineengine comprising: a stage of guide vanes; a compressor downstream fromthe stage of guide vanes; a combustor downstream from the compressor,the combustor comprising a primary combustion zone and a secondarycombustion zone downstream from the primary combustion zone, wherein theprimary combustion zone comprises an exit configured to channelcombustion gases towards the secondary combustion zone, wherein thecombustor is operable in a plurality of combustion modes; and acontroller communicatively coupled to the stage of guide vanes, thecontroller configured to: monitor a temperature at the exit of theprimary combustion zone; determine a combustion mode in which thecombustor is operating; and selectively open and close the guide vanesto facilitate maintaining the temperature at a temperature thresholdassociated with the combustion mode in which the combustor is operating.10. The gas turbine engine in accordance with claim 9, wherein thecombustor is operable in a plurality of combustion modes, the controllerfurther configured to facilitate maintaining the temperature within arespective predefined temperature range that is associated with eachcombustion mode.
 11. The gas turbine engine in accordance with claim 9,wherein the controller is further configured to calculate thetemperature at the exit of the primary combustion zone.
 12. The gasturbine engine in accordance with claim 11, wherein the controller isfurther configured to calculate the temperature based on an airflowoutput from the compressor, a fuel flow input to the combustor, and anoperational status of an inlet bleed heat system.
 13. The gas turbineengine in accordance with claim 9 further comprising a fuel injectionsystem comprising a primary fuel injector configured to provide fuel tothe primary combustion zone, and a secondary fuel injector configured toprovide fuel to the secondary combustion zone.
 14. The gas turbineengine in accordance with claim 9, wherein the controller comprises atleast one of a Proportional controller or a Proportional-Integral (PI)controller.
 15. A method of controlling emissions from a gas turbineengine that includes a compressor and a combustor, the methodcomprising: monitoring a temperature within the combustor of the gasturbine engine, wherein the combustor includes a primary combustion zoneand a secondary combustion zone downstream from the primary combustionzone, the temperature monitored at an exit of the primary combustionzone; determining a combustion mode in which the combustor is operating;and selectively opening and closing guide vanes upstream of thecompressor to facilitate maintaining the temperature at a temperaturethreshold associated with the combustion mode in which the combustor isoperating.
 16. The method in accordance with claim 15, whereindetermining a combustion mode comprises determining the combustion modebased on physical conditions within the combustor.
 17. The method inaccordance with claim 16, wherein monitoring a temperature comprisescalculating the temperature based on an airflow output from thecompressor, a fuel flow input to the combustor, and an operationalstatus of an inlet bleed heat system.
 18. The method in accordance withclaim 16, wherein the combustor is operable in a plurality of combustionmodes, the method further comprising maintaining the temperature withina respective predefined temperature range that is associated with eachcombustion mode.
 19. The method in accordance with claim 15 furthercomprising controlling operation of the guide vanes with at least one ofa Proportional controller or a Proportional-Integral (PI) controller.20. The method in accordance with claim 15, further comprisingcontrolling operation of an inlet bleed heat system to facilitatemaintaining the temperature at the desired temperature threshold.